1. Field of the Invention
The present invention relates to a connecting construction of a flat panel display device such as a liquid crystal display device and a drive circuit substrate thereof and, particularly, to a flat panel display device having a construction, in which a display panel provided with a plurality of TCP""s (Tape Carrier Packages) is easily detachably mounted on a casing of the flat panel display device, and a manufacturing method thereof.
2. Description of the Prior Art
As a flat panel display device, a liquid crystal display device, a plasma display device and an electroluminescence device, etc., are well known and, particularly, the liquid crystal display device has been used widely as a display of a mobile information terminal, a notebook type personal computer, and a home use word processor, for which the portability is required.
As a typical example of the flat panel display device, the liquid crystal display device will be described. With the recent tendency of reduction of size and weight of an electronic device on which a liquid crystal display device is mounted, a further reduction of size of the liquid crystal display device is required. Particularly, reduction of an area of the liquid crystal display device except an image display region thereof, that is, a frame portion of the liquid crystal display device, and reduction of thickness of the liquid crystal display device itself are important problems to be solved.
In order to drive the liquid crystal display device, semiconductor driver elements each in the form of such as LSI, etc., called xe2x80x9cdriver LSI""sxe2x80x9d are required. In order to achieve the reduction of size of liquid crystal display device, a COG (Chip On Glass) method for directly forming the driver LSI on a display panel substrate has been developed. However, if the driver LSI directly formed on the display panel substrate is defective, the whole panel substrate becomes defective. In order to solve such problem, it has been usual to arrange a driver LSI on each TCP (Tape Carrier Package) by using TAB (Tape Automated Bonding) so that the driver LSI""s are connected to a display panel substrate through the TCP""s.
The TCP manufactured by using the TAB includes a plurality of lead electrodes, which are connected to protruded electrodes, called xe2x80x9cbumpsxe2x80x9d, of the LSI called xe2x80x9cbare chipxe2x80x9d. The lead electrodes on the side of the display panel or the circuit substrate are called as xe2x80x9couter leadsxe2x80x9d and those on the side of the LSI are called as xe2x80x9cinner leadsxe2x80x9d. The lead electrodes comprise a number of stripe-shaped electrodes formed by patterning a copper foil formed on an insulating base film of such as polyimide, etc. In order to highly reliably connect the LSI by contacting the bumps of the LSI to the inner leads under pressure, the base film is made thick enough to provide a sufficient mechanical strength thereof during the pressure-contact step.
Therefore, when the TCP having one end connected to the display panel is bent to fit it to a suitable holding member provided on a chassis of the display device, the bending operation is facilitated by forming a slit or slits in only a portion or portions of the TCP at which the latter is bent to form a rounded portion thereof. Japanese Patent No. 2616564 and Japanese Patent Application Laid-open No. H9-265104 disclose examples of a liquid crystal display device employing TCP""s each having such slit or slits and a flexible portion.
Particularly, in the liquid crystal display device disclosed in Japanese Patent Application Laid-open No. H9-265104, a liquid crystal panel is held by a lock member such as protrusions provided on a chassis and circuit substrates each connected to a plurality of TCP""s are held by hook portions provided on a side surface of the casing. With such construction, an assembling and disassembling of the liquid crystal display device are facilitated.
When this construction in which the circuit substrates and the display panel are merely held in positions without using adhesive, there is a merit that, when a liquid crystal panel becomes failure, an exchange of the liquid crystal panel with a new panel is facilitated.
However, in order to hold the circuit substrate by the hook portions, it is necessary to pull up the circuit substrate and then insert them into insides of the hook portions. In a case where circuit substrates are fixed to side surfaces of a chassis by adhesive, it is enough to merely bend TCP""s at slit portions thereof so that a length of each TCP may be minimum. In the hooking type construction, which requires the pull-up step of the TCP""s and the insertion step thereof into the hook portions, the length of each TCP is increased by an amount necessary for pulling the TCP up. Further, a peeling stress is generated in the connecting portion between the display panel and the TCP when the latter is pulled up. In addition, since the increased length portions of the TCP""s are risen up from a plain of the connecting portion after the circuit substrate is hooked in the hook portions, it is necessary to provide a space for receiving the risen portion of the TCP.
Since the liquid crystal display device is usually used as a display of a portable information terminal, a notebook type personal computer or a home-use word processor, etc., the liquid crystal display device has to be not only highly compact but also durable against vibration and thermal shock. On the other hand, since, when the size of liquid crystal display panel is increased, the liquid crystal display panel may be deformed due to thermal expansion of the panel itself, the adhesive is usually not used to fix the liquid crystal panel to the chassis. Instead thereof, the liquid crystal panel is supported by only the hooking members as mentioned previously. The size of the liquid crystal panel and the positioning of the hooking members mounted on the chassis are determined by taking the fact that there are unavoidable machining errors (about several tenth millimeters each) of the liquid crystal panel and the chassis into consideration. That is, in order to improve the product yield of the flat panel display device, it is usual to design the size of the liquid crystal panel and the positioning of the hooking members mounted on the chassis such that the length of the hooking members mounted on the chassis is slightly larger than an ideal size of the liquid crystal panel in order to allow the liquid crystal panel to be reliably fitted in the chassis. Therefore, in a finished liquid crystal display device, there may be a case where the liquid crystal panel slightly moves with respect to the casing.
With such movement of the liquid crystal panel with respect to the casing, a stress is exerted on the TCP""s connected to the liquid crystal panel, so that there is a possibility that a connection in the pressure-contacted portion between the circuit substrate and the TCP""s and a connection in the pressure-contacted portion between the liquid crystal panel and the TCP""s are broken. It is difficult to absorb such stress by only the slit provided in only the rounded portion of each TCP.
In the technique disclosed in Japanese Patent Application Laid-open No. H9-265104, a rounded portion of a TCP is received between a frame and a liquid crystal panel by pulling a flexible portion of the TCP up to a vicinity of an upper surface of the liquid crystal panel and then bending it down such that the rounded portion of the TCP has a large radius of curvature even after a circuit substrates are held by hook portions of a chassis.
Therefore, in view of prevention of peeling-off due to bending stress of the TCP caused by reduction of the size of liquid crystal display device, the provision of the rounded portion having large radius of curvature is meaningful. However, in view of further reduction of thickness and size of the flat panel display device, the structure has to be improved further. Further, in the construction, in which the TCP has such large rounded portion, the total length of the TCP is large. However, the length of the TCP should be as short as possible in view of high frequency characteristics of the display device.
For a reference purpose only, the above mentioned breaking phenomenon of the connection will be described with reference to FIGS. 1A to 1C, which show the steps of mounting a liquid crystal panel and a circuit substrate on a casing. A liquid crystal panel 1 is held on a main surface of a casing 4, as shown in FIG. 1A. Then, each TCP 2 is bent at a slit 7, which is provided in a region thereof to be rounded, along a ridge portion of the casing as shown in FIG. 1B and a circuit substrate is held in a hook portion 6 provided on the side surface of the casing 4 as shown in FIG. 1C.
As shown in FIG. 1B, in holding the circuit substrate 3 in the hook portion 6, it is necessary to pull up the rounded portion of the TCP""s 2. When the TCP""s 2 is pulled up in such manner, loads acting in opposite directions to peel off the TCP""s 2 from the liquid crystal panel 1 are exerted on the junctions between the TCP""s 2 and the liquid crystal panel 1, with which lead lines in the junctions may be broken.
Furthermore, in pulling the TCP""s 2 up, loads are also exerted on connecting portions between the TCP""s 2 and the circuit substrate 3, with which the connection between the TCP""s 2 and the circuit substrate 3 may be broken.
The above-mentioned problems may also occur in other flat panel type display devices.
In view of the state of art mentioned above, an object of the present invention is to provide a flat panel display device having a connecting construction of each of TCP""s, whose length is limited to a necessary minimum to reduce a size of a rounded portion thereof to thereby make thickness and size thereof possible to further reduce and a method for manufacturing the same flat panel display device.
The present invention is achieved on the basis of not a mere construction required by the rounded portions of the TCP""s after the display device is completed. That is, the inventors of the present invention have studied the mechanism of stress generation in a TCP in the bending step of a slit of the TCP to form a rounded portion slit and found that a peel-off stress not only during an assembling operation of the display device but also after the completion of the display device can be relaxed without requiring an extra length of the TCP by newly providing an auxiliary slit in the TCP, which is bent during the assembling operation and returns to a flat state after the display device is completed. The present invention is achieved on the basis of the above-mentioned discovery.
That is, according to the present invention, a flat panel display device is featured by comprising a chassis, a display panel put on a main surface of the chassis, a circuit substrate held in a hook portion provided on a side surface of the chassis and a plurality of TCP""s having one ends connected to the display panel and the other ends connected to the circuit substrate, each TCP having a first region extending substantially in parallel to a main surface of the chassis, a second region extending substantially in parallel to a side surface of the chassis, a rounded region between the first region and the second region and a third region provided in at least one of the first and second regions and extending in parallel to the extending direction of the rounded region, the third region having a higher flexibility than that of the at least one of the first and second regions.
That is, the TCP employed in the present invention includes not only an easily deformable region, which is easily bent and provided for the rounded portion, but also the auxiliary slit, which is temporarily bent. The slit for rounded portion will be referred to as xe2x80x9cmain slitxe2x80x9d and the auxiliary slit will be referred to as xe2x80x9csub slitxe2x80x9d.
Furthermore, the present invention is featured by that the rounded region of the TCP in which the main slit is formed is positioned in a level lower than a surface level of the first region.
Moreover, the present invention is featured by that the TCP further has a driver element-connecting region and the third region is constructed with a plurality of lead lines covered by a flexible insulating film thinner than an insulating film in the vicinity of the driver element-connecting region.
The present invention is further featured by that the display panel is loosely fitted on the chassis such that a relative mechanical displacement of the display panel to the chassis is absorbed in the third region.
Furthermore, in the flat panel display device of the present invention, the sub slit of the TCP may be provided in the first region and connected to the main slit in the rounded region to form a wide slit.
It is preferable that a distance between a center of the main slit and a center of the sub slit is preferably larger than a depth of the hook portion.
Moreover, a main body of the TCP of the present invention is constructed with a plurality of lead lines covered by an insulating flexible film and the main and sub slits extend in directions perpendicular to the extending direction of the TCP from the liquid crystal panel to the circuit substrate, respectively, the main and sub slits being constructed with the plurality of the lead lines covered by an insulating flexible coating member thinner than the insulating flexible film constituting the main body of the TCP.
According to the present invention, a method for manufacturing a flat panel display device is also provided, which method is featured by comprising the steps of holding a display panel having TCP""s connected to a circuit substrate on a chassis, pulling up the circuit substrate by bending each TCP at a main slit for forming a rounded portion and a sub slit provided in the TCP such that a lower edge of the circuit substrate exceeds front edge of hook portion provided on the chassis and inserting the circuit substrate into the hook portion by returning the sub slit to an original flat state.
Particularly, the sub slit is featured by that it is provided between the main slit and the display panel and a bending direction of the sub slit in the step of pulling up the circuit substrate is opposite to a bending direction of the main slit.
Alternatively, the sub slit is featured by that it is provided between the main slit and the display panel and a bending direction of the sub slit in the step of pulling up the circuit substrate is the same as a bending direction of the main slit.
Alternatively, the sub slit is featured by that it is provided between the main portion slit and the display panel and is connected to the main slit to form a wide common slit and that a bending direction of the common slit in the vicinity of the circuit substrate in the step of pulling up the circuit substrate is opposite to a bending direction of the main slit in the vicinity of the display panel.
Particularly, the method for manufacturing a flat panel display device is featured by that the display panel is loosely fitted on the chassis.
In the present invention having such features, the load exerted on the TCP is absorbed by not only the main slit region but also the sub slit region, which is temporarily bent during the assembling operation. Therefore, when the liquid crystal panel or the circuit substrate moves on the chassis, it is possible to reduce the load exerted on the TCP by the main and sub slits. Consequently, it is possible to prevent the connection between the liquid crystal panel and the circuit substrates from being broken during the mounting of the circuit substrate and the circuit in the TCP from being broken during a vibration test or a shock test of the liquid crystal display device. Furthermore, according to the present invention, it is possible to reduce the number of assembling steps of the liquid crystal display device and the number of parts thereof to be assembled.